1. Field of the Invention
The present invention relates to a photosensor for detecting optical information, or a photosensor which is well suited to detect radiations, such as X-rays and xcex3-rays, directly or after converting the wavelength regions thereof into the photosensitive wavelength region such as that of visible light. It also relates to a radiation detection apparatus and system each of which is constructed by adopting the photosensor.
2. Related Background Art
Heretofore, a film has generally been used for observing a radiation transmission image in a radiation diagnosis. Besides, an image intensifier (hereinbelow, expressed as xe2x80x9cI/Ixe2x80x9d) has been used in order to observe a transmission image in real time during the irradiation of radiation. The I/I, however, has had the problems of a large size and a heavy weight.
Recently, a large-sized sensor employing amorphous silicon (hereinbelow, expressed as xe2x80x9ca-Sixe2x80x9d) has been proposed as a detector which is smaller in size and lighter in weight and with which a transmission image can be observed in real time. This sensor has a construction wherein a photodiode being a light receiving element formed of the a-Si, and a thin film transistor (hereinbelow, abbreviated to xe2x80x9cTFTxe2x80x9d) being a switching element are combined in one-to-one correspondence so as to form one pixel, and wherein the light receiving elements formed of the a-Si are arrayed in the shape of a two-dimensional matrix (see, for example, U.S. Pat. No. 5,262,649).
Although the above photodiode is of pin type, photodiodes include ones of pn type, Schottky type, etc. In addition, a photosensor of MIS type has been proposed by the inventors of the present invention (see the official gazette of Japanese Patent Application Laid-Open No. 8-116044). In this photosensor, a transparent electrode is disposed on an entrance side for light, and a wiring line Vce for the common electrode in the sensor is formed of metal. The common electrode line Vce is laid passing parts of the upper portions of the photodiodes, in parallel with signal lines Vsig which transfer light signals from the photodiodes to an amplifier via the switching TFTS.
Herein, the metal employed for the common electrode in the sensor is one which is opaque to light (for example, Al, Cr, W, Ta or Mo). In consequence, the common electrode line Vce conceals the light receiving portions of the photodiodes and lowers the opening degree of these portions, thereby to decrease light inputs to the light receiving areas of the photodiodes and to degrade the S/N (signal-to-noise) ratios of the light signals.
The present invention has its object to provide a photosensor in which, in spite of a large screen and a high definition, the opening degree of a light receiving portion can be held higher, thereby to increase a light input to this portion and to ensure a good S/N ratio.
Another object of the present invention is to provide a radiation detection apparatus and a radiation detection system each of which adopts the above photosensor, especially a two-dimensional photosensor in which light receiving elements are arrayed in two dimensions.
In one aspect of performance of the present invention, there is provided a photosensor having a plurality of pixels each of which includes a light receiving element and a switching element, a common electrode line to which one of a pair of electrodes of each of the light receiving elements is connected in common with each of the pixels, and signal lines to which light signals of the light receiving elements are transferred by simultaneously driving the switching elements of the pixels. A main wiring portion of said common electrode line is formed over said signal lines.
In another aspect of performance of the present invention, there is provided a radiation detection apparatus wherein a photosensor has a plurality of pixels each of which includes a light receiving element and a switching element, a common electrode line to which one of a pair of electrodes of each of the light receiving elements is connected in common with each of the pixels, and signal lines to which light signals of the light receiving elements are transferred by simultaneously driving the switching elements of the pixels. The photosensor is overlaid with wavelength conversion means for converting a wavelength region of radiation into a sensible wavelength region of the light receiving elements. A main wiring portion of the common electrode line is formed over the signal lines.
In a further aspect of performance of the present invention, there is provided a radiation detection system comprising a radiation detection apparatus including a photosensor having a plurality of pixels each of which includes a light receiving element and a switching element, a common electrode line to which one of a pair of electrodes of each of the light receiving elements is connected in common with each of the pixels, and signal lines to which light signals of the light receiving elements are transferred by simultaneously driving the switching elements of the pixels and over which a main wiring portion of the common electrode line is formed. The system also includes wavelength conversion means disposed over the photosensor, for converting a wavelength region of radiation into a sensible wavelength region of the light receiving elements, and image processing means for processing image information delivered for the radiation detection apparatus.